This invention relates to the field of AM stereophonic receivers and, more particularly, to the control of various functions within the receivers in response to negative overmodulation levels of the received signal, signal strength, detection of a pilot tone or to externally applied control signals.
As AM stereo receivers developed, it became increasingly apparent that a number of functions within the receivers could be improved by the addition of some degree of control in response to the quality of the received signals. In the above-referenced patent, U.S. Pat. No. 4,688,254, a voltage was developed and stored in response to the detection of negative modulation in the in-phase signal. As is known, such modulation is due primarily either to noise in the trough of the modulation or to interfering signals, but not to a modulating program signal. At a predetermined level of the stored voltage the amount of correction applied to signals requiring a form of correction was reduced and, if the excessive modulation continued to increase, to reduce the amount of stereo information in the audio outputs, (a function commonly called blend). This same voltage source has been determined to be usable for controlling other functions within the receiver, as well as being controlled by other conditions.